1. Field of the Invention
The invention generally relates to electrical circuit design, and more particularly to a digital-to-analog converter using tunneling current characteristics of a field effect transistor (FET) ultra-thin gate oxide.
2. Description of the Related Art
Analog-to-digital converters convert analog signals such as speech, music, and video and transform it into a digital form, which can be more readily processed by most conventional computers and microprocessors. A typical analog-to-digital converter is the parallel encoder, which utilizes a bank of voltage comparators and a bank of resistors to simultaneously compare an analog input signal to a set of reference voltages.
These devices usually comprise a stable reference voltage and a series of equal resistors, which form a voltage-dividing sequence between the reference voltage and ground. For example, for a 3-bit converter, 2x=number of resistors used, where x=3 for a 3-bit converter, thus 23=8 resistors are used. These devices further include a set of voltage comparators, which for the 3-bit converter example would require 231=7comparators. Also, these devices include an encoder circuit, which reads the comparator outputs (high or low voltage), and produces a 2-bit binary output for each comparator.
Similarly, digital-to-analog converters take a binary input and convert it into an analog form using a stable reference voltage, a connection of resistors referred to as a ladder (for example, an R−2R ladder), a series of FET switches, and operational amplifier output circuitry.
Conventionally, digital-to-analog converters use banks of large resistors to make voltage dividers for each bit of a digital input. The resistors have higher than desired tolerance and require large areas for layout as well as power consumption. Moreover, the conventional digital-to-analog converters are subject to several errors including saturation errors, resolution and quantization errors, and conversion errors.
Therefore, due to the limitations of the conventional devices, there is a need for a novel digital-to-analog converter, which provides an accurate voltage divider and overcomes the drawbacks of the conventional devices.